Diesel Engine Emissions During High EGR Operation

由于其高燃料经济性，柴油发动机广泛用于道路应用。在满足日益严格的排放法规的同时保持效率和性能的需求迫使发动机开发人员设计出先进的缸内燃烧策略，以在特定工况下最大限度地减少排放并最大限度地提高性能。这些策略目前受到高排放和性能差的限制，因为发动机的速度和负载在瞬态操作期间发生变化。即使在广泛的稳态燃烧条件下，对发动机负荷、充气条件和充气成分对燃烧过程的影响也缺乏基本的了解。瞬态试验提供了发动机工作模式变化的影响信息。这些测试的结果对于所使用的发动机、空气交换和控制系统是高度特定的;也可能难以识别与燃烧事件相关的因果关系。因此，虽然这些试验对发动机研制是必要的，但它们不能提供在本项目中寻求的改进的基本理解所需的信息。因此，本项目将采用控制良好的稳态发动机试验，所选择的运行条件代表瞬态运行期间单个发动机循环遇到的充气条件。将测量进气流和排气流中空气成分的循环间变化，并将其与燃烧过程中观察到的变化进行比较。通过各种试验，包括使用点火促进剂，可以对燃烧不稳定性的主要原因进行评价。燃烧不稳定性导致发动机性能差和未燃燃料排放量高。高EGR率是影响柴油机排放控制的主要因素之一。许多新的柴油发动机喷射系统具有在一个燃烧循环内喷射燃料多次的潜力。该项目将使用新开发的高EGR操作的基本理解，以确定新的喷射策略，可以提高燃烧性能。优化过程将被用来确定最有前途的潜在策略，在一系列发动机运行条件下，类似于那些在瞬态操作过程中遇到的。该项目将涉及两名博士研究生（其中一人将由拉夫堡大学资助）在PI的密切监督下工作。由经验丰富的学术和工业发动机研究人员组成的顾问小组将为该项目提供指导。技术支持将由熟练的研究技术人员提供。该研究将在新安装的最先进的汽车尺寸单缸研究发动机上进行。整个项目的方法将涉及首先确定在低温（高EGR）和常规（低EGR）柴油燃烧之间的过渡模式转换期间将遇到的操作条件。然后，将在一系列条件下进行稳态发动机试验，这些条件代表瞬态运行期间遇到的充气成分和EGR水平。基于这些实验结果，将更详细地研究那些表现出高排放和/或燃烧稳定性差的操作条件，包括光学缸内评估和循环分辨排放测量。燃烧增强器将被用来研究在高EGR水平的动力学限制的影响。最后，一系列的多次喷射策略将进行评估，以确定高EGR瞬态操作下的排放控制技术。

Due to their high fuel economy, diesel engines are widely used in on-road applications. The need to maintain efficiency and performance while meeting increasingly stringent emissions regulations is forcing engine developers to design advanced in-cylinder combustion strategies tailored to minimize emissions and maximize performance at specific operating conditions. These strategies are currently limited by high emissions and poor performance as the engine's speed and load change during transient operation. Even under a wide range of steady-state combustion conditions, there is a shortage of fundamental understanding of the effects of the engine load, charge conditions and charge composition on the combustion process.Transient tests provide information on the effects of a change in the operating mode of an engine. The results of such tests are highly specific to the engine, air exchange, and control system used; it can also be difficult to identify cause and effect relationships relating to the combustion event. As a result, while such tests are necessary for engine development, they do not provide the information needed to develop the improved fundamental understanding being sought in this project. Therefore, this project will adopt well controlled steady-state engine tests with the operating conditions selected to be representative of the charge conditions encountered by individual engine cycles during transient operation. Cycle-to-cycle variability in the composition of the air in the intake and exhaust streams will be measured and will be compared to the observed variability in the combustion event. A variety of tests, including the use of an ignition promoter, will permit evaluation of the principal causes of combustion instability.Combustion instability leads to poor engine performance and high unburned fuel emissions. It is one of the key barriers to the application of high EGR strategies to control diesel engine emissions. Many new diesel engine injection systems have the potential to inject fuel several times within one combustion cycle. This project will use the newly developed fundamental understanding of high-EGR operation to identify novel injection strategies that can improve combustion performance. An optimization process will be used to identify the most promising potential strategies over a range of engine operating conditions similar to those encountered during transient operation. This project will involve two PhD research students (one of whom will be funded by Loughborough University) working under the close supervision of the PI. An advisory panel composed of experienced academic and industrial engine researchers will provide guidance for the project. Technical support will be provided by skilled research technicians. The research will be conducted on a newly installed, state-of-the-art automotive-sized single-cylinder research engine. The overall project methodology will involve first identifying the operating conditions which will be encountered during a transitional mode-shift between low temperature (high EGR) and conventional (low EGR) diesel combustion. Then, steady-state engine tests will be conducted over a range of conditions which are representative of the charge composition and EGR levels encountered during transient operation. Based on these experimental results, those operating conditions which demonstrate high emissions and/or poor combustion stability will be investigated in more detail, including optical in-cylinder evaluation and cycle-resolved emissions measurements. A combustion enhancer will be used to investigate the effects of kinetic limitations at high EGR levels. Finally, a range of multiple-injection strategies will be evaluated to identify techniques for controlling emissions under high-EGR transient operation.